Rolling bearings are used widely in a variety of machines because rolling bearings, as compared with sliding bearings, cause small friction loss. Effective damping action for damping the vibration of a rolling bearing when rotating speed rises beyond a critical speed can be scarcely expected from the rolling bearing in view of the construction of the rolling bearing. Therefore, a damper is incorporated into a rolling bearing to provide the rolling bearing with a vibration damping ability in order to reduce vibrations of a machine and dynamic load on the rolling bearing and to extend the life of the bearing.
A squeeze film damper is used in combination with the rolling bearing.
The squeeze film damper is applied to the outer circumference of the bearing. The damping effect of a squeeze film of a fluid lubricant damps the vibration of the bearing.
The squeeze film damper applied to the outer circumference of the bearing can exercise a necessary damping ability without changing the intrinsic tribological characteristic of the bearing.
Generally, the dynamic characteristic of a damping oil film is a function of eccentricity ratio. In a state where a damper journal is moved aside such that the eccentricity ratio is nearly equal to 1.0, the dynamic characteristic of the damping oil film has strong nonlinearity and it is difficult to design a proper damper.
Therefore, a squeeze film damper including an axially disposed cage-shaped centering spring as shown in FIG. 9 is used widely. The centering spring centers the journal of the shaft so that the axis of the journal approaches the axis of the damper and a damping oil film is formed around the journal in a uniform thickness and the eccentricity ratio approaches zero. When the journal is thus centered and the dynamic characteristic of the damping oil film is in a range of weak nonlinearity, the dynamic characteristic of the damping oil film when the eccentricity ratio is approximately zero can be used and hence the damper can be comparatively easily designed.
Since the cage-shaped centering spring is disposed axially, the squeeze film damper has complicated construction and is large. Therefore, the squeeze film damper has been applied only to limited machines, such as turbines.
A squeeze film damper bearing disclosed in Patent document 1 is provided with a centering spring inserted into a space between a bearing supporting a rotating shaft and a bearing case. The centering spring is in a thin stainless steel strip provided with protrusions of the same height formed by press working. The centering spring is bent in a cylindrical shape. The centering spring formed in a cylindrical shape is fitted in a groove formed in the inner circumference of the bearing case to support the bearing elastically such that a space of a thickness between 0.1 and 0.2 mm is formed between the outer circumference of the bearing and the bearing case. Oil is supplied into the space to form an oil film capable of damping the whirling motion of the rotating shaft.
The method, as compared with other known methods, can make the squeeze film damper bearing at a low cost, can form a centering spring having a desired spring stiffness selected from a wide range of spring stiffness. However, the method that forms the plurality of protrusions by press working has difficulty in forming the protrusions accurately in the same height and in designing and fabricating a centering spring having a desired rigidity.
Patent document 1: JP 11-2240 A